Anatomy of a function - Python

Functions work very similarly in whatever language you might use, i.e. they have the same component parts. What changes is the syntax used to describe those.

For example, in python a function is created using the following syntax:

Anatomy of a function - R

If we look at the anatomy of a R function instead, we can see that the same things are present - we still need to declare that we are creating a function, we still need to assign a name, we can still provide parameters and we have a body that does the work too.

Anatomy of a function - JavaScript

Finally, let’s look at a JavaScript function. It is similar to both the Python and R function declarations, but also has some notable differences from either. However, the differences are cosmetic - once you know how to dissect and interpret a function in one language, it is much easier to do that in whatever syntax they are presented.

Differences in anatomy

So what are the differences between these? The order in which things are done and the notation used: In Python we start by declaring that we want to create a function, whereas in R we assign the function’s name first. But despite these differences they are doing the same thing.

def simpleAddition(a, b):
  return print(a + b)

simpleAddition(5, 6)

11

simpleAddition <- function(a, b){
  return(print(a + b))
}

simpleAddition(5, 6)

[1] 11

Built-in functions

All languages come with oven-ready functions available - you may have even used some already!

The code on this slide shows how you find the length of a string in Python and R respectively. These are built-in functions, but they operate exactly the same as ones you make yourself - they are called, they take an argument and they return a result.

str_len = len("Function lovers unite")
print(str_len)

21

str_len <- nchar("Function lovers unite")
print(str_len)

[1] 21

Time for some coding

We’re about to switch to VS Code. If you are reviewing this after the event, the relevant files should be with this presentation.

Questions on functions?

Conditional Statements

You will likely be familiar with these sorts of logical statements already - IF something is true then do this, ELSE do this. These tell the computer to execute certain parts of the code, provided specified conditions are met. They are the core of decision-making in programming, and as such are vital if you want to make good use of your chosen language.

Conditional Statements - Python

As with functions, conditional statements work very similarly in whatever language you are using - what changes is the syntax. Python uses its standard colon + indentation to indicate what code will be executed.

Conditional Statements - R

The logic for R is the same, but it also follows the language’s regular syntax. This means that your conditions will be contained in brackets instead of preceding a colon and statements are contained in curly brackets.

Conditional Statements - JavaScript

JavaScript actually has the exact same syntax as R, which makes it nice and easy to follow if you are used to that already. Just bear in mind that how you declare variables and comments is different, as per the example here.

Loops

Loops are simply an instruction to repeatedly execute a block of code until a specified condition is met, a process known as Iteration.

Loops are essential to efficient and organised programming and exist in almost every programming language, so you will almost certainly come across them as you become more proficient with your language of choice.

For loops

For loops exist to allow iteration to occur a specific number of times, iterating through things that have a definite length or size. If you have 1000 things that need evaluating, rather than write 1000 lines of code you would use one of these.

They are probably the loop you will use the majority of the time, because the usual things you will need to repeatedly act on will be an array/list/vector etc.

While loops

While loops will run until a condition is satisfied - they do not have to have a defined number of iterations. This is useful when you don’t know or can’t determine the number of iterations, want to give users a choice to end a program or any other circumstance where your program is required to run without stopping until something happens.

But be careful - if the condition is not met the loop could potentially run infinitely, which can cause a lot of problems in some contexts.

Loops in Python

Loops in R

Loops in JavaScript

Time for some more coding

We’re about to switch to VS Code. If you are reviewing this after the event, the relevant files should be with this presentation.

Questions on control flow?